Chris Grayling, who said he was 'strengthening the current law' protecting people who attack intruders. Photograph: Oli Scarff/Getty Images

The new justice secretary's announcement that he will let householders deploy "disproportionate" force defending homes and families has been greeted by criminal lawyers with dismay.

Chris Grayling's determination to reform the frequently reviewed laws of self defence was described as a vote-catching initiative that will be difficult to translate into legislation.

Speaking at the Conservative party conference in Birmingham, Grayling said: "Being confronted by an intruder in your own home is terrifying, and the public should be in no doubt that the law is on their side. That is why I am strengthening the current law.

"Householders who act instinctively and honestly in self defence are victims of crime and should be treated that way. We need to dispel doubts in this area once and for all."

The current law already allows people to use "reasonable force" to defend themselves (either at home or on the street), to protect others, to prevent crime or to protect property.

Section 76 of the Criminal Justice and Immigration Act 2008 says the degree of force used in self-defence must be "reasonable in the circumstances" as the person acting genuinely believed them to be.

The justification of acting "honestly and instinctively", taken from one key judgment widely relied upon, is already embedded in Crown Prosecution Service guidance.

But the justice secretary wants to change the definition. Use of "disproportionate force" is not currently lawful. Grayling will allow householders to use force that they "believed was reasonable in the circumstances but was actually disproportionate when viewed with the benefit of hindsight", the Ministry of Justice said.

The recent case that revived interest in self-defence laws involved Andy and Tracey Ferrie, who used a legally held shotgun to defend their remote Leicestershire cottage. The intruders were injured. The Ferries were held for 40 hours by police but were not charged.

There are relatively few prosecutions of householders who use force against intruders. An informal trawl by the CPS suggests that between 1990 and 2005 there were only 11 prosecutions of people who attacked intruders in houses, commercial premises or private land. Only seven of those resulted from domestic burglaries.

Householders who defend themselves against burglars should not be expected to exercise "calm cool judgment", he explained. "You are not calmly detached. You are probably very cross and very frightened – a mixture of both … the householder is entitled to use all sorts of reasonable force to get rid of the burglar."

Responding to Grayling's initiative, Michael Turner QC, chair of the Criminal Bar Association, said: "It's a vote-catcher. There's no concept elsewhere in British law of allowing anyone to use disproportionate force for pretty obvious reasons.

"It's no surprise that a non-lawyer [Grayling] would come up with such a crazy idea. Are we really saying that the police should not even investigate cases [where an intruder has been injured]? I can't believe this will make it into statute."

Richard Atkinson, the chair of the Law Society's criminal committee, which represents solicitors, said: "Whatever he comes up with will have to be very clear to be well defined. Grayling is setting himself a difficult task.

"Will it apply to commercial property as well as homes? There needs to be consultation on it. It will have judicial consequences in many other areas."

Maura McGowan QC, vice-chairman of the Bar Council, said: "The law on self defence is perfectly clear. Householders are fully entitled to use proportionate force to defend themselves and their property, which is a principle which we support. At a time when fundamental principles of open justice are under threat from ill-considered legislation and severe cuts, it is regrettable that chasing populist headlines is top of the new justice secretary's agenda."

Another criminal barrister, David Farrer QC, was equally dismissive of the proposal. "Once again another government is pledging to reform self-defence laws," he said. "We have seen the same populist sentiments from successive governments. However, the realities are that there is no need to reform the current laws.

"In practice, the application of the reasonable force test is perfectly straightforward and is applied to facts of each individual case. The CPS in recent years has caught the mood of the country and is making sensible decisions on bringing prosecutions in self-defence incidents."

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